Observation of quantum capacitance in the Cooper-pair transistor

We have fabricated a Cooper-pair transistor (CPT) with parameters such that for appropriate voltage biases, it behaves essentially like a single Cooper-pair box (SCB). The effective capacitance of a SCB can be defined as the derivative of the induced charge with respect to gate voltage and has two p...

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Bibliographic Details
Published in:Physical review letters 2005-11, Vol.95 (20), p.206807.1-206807.4, Article 206807
Main Authors: DUTY, T, JOHANSSON, G, BLADH, K, GUNNARSSON, D, WILSON, C, DELSING, P
Format: Article
Language:English
Subjects:
Applied sciences
Classical and quantum physics: mechanics and fields
Electronics
Exact sciences and technology
Physics
Quantum computation
Quantum information
Semiconductor electronics. Microelectronics. Optoelectronics. Solid state devices
Superconducting devices
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Summary:We have fabricated a Cooper-pair transistor (CPT) with parameters such that for appropriate voltage biases, it behaves essentially like a single Cooper-pair box (SCB). The effective capacitance of a SCB can be defined as the derivative of the induced charge with respect to gate voltage and has two parts, the geometric capacitance, C(geom), and the quantum capacitance C(Q). The latter is due to the level anticrossing caused by the Josephson coupling and is dual to the Josephson inductance. It depends parametrically on the gate voltage and its magnitude may be substantially larger than C(geom). We have detected C(Q) in our CPT, by measuring the in phase and quadrature rf signal reflected from a resonant circuit in which the CPT is embedded. C(Q) can be used as the basis of a charge qubit readout by placing a Cooper-pair box in such a resonant circuit.
ISSN:0031-9007
1079-7114
DOI:10.1103/physrevlett.95.206807